With fallback depending on chainparams: this means the first upgrade
will be slow, but after that it'll be fast.
Fixes: #990
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
It's just a sha256_double, but importantly when we convert it to a
string (in type_to_string, which is used in logging) we use
bitcoin_blkid_to_hex() so it's reversed as people expect.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Google lead me to a discussion about litecint, it suggested they would use
'ltc' and I don't really care.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
